Fix API dev: use pip editable install instead of uv run

uv run spawns uvicorn, which uses multiprocessing.spawn for hot reload.
The spawned subprocess starts a fresh Python interpreter that bypasses
uv's venv activation — so it never sees the venv's packages.

Fix: use a standalone python:3.12-slim dev stage with pip install -e .
directly into the system Python. No venv means the spawn subprocess uses
the same interpreter with the same packages. The editable install creates
a .pth file pointing to /app/src, so the mounted host source is live.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/Dockerfile

@@ -2,14 +2,15 @@ FROM python:3.12-slim AS base
 WORKDIR /app
 RUN pip install uv
 
-FROM base AS development
-# python:3.12-slim has no bare 'python' binary; without this uv invalidates the baked venv on every start
-RUN ln -sf /usr/local/bin/python3 /usr/local/bin/python
+FROM python:3.12-slim AS development
+WORKDIR /app
 COPY pyproject.toml .
 COPY src/ src/
-RUN uv sync
-COPY . .
-CMD ["uv", "run", "uvicorn", "rehearsalhub.main:app", "--host", "0.0.0.0", "--port", "8000", "--reload"]
+# Install directly into system Python — no venv, so uvicorn's multiprocessing.spawn
+# subprocess inherits the same interpreter and can always find rehearsalhub
+RUN pip install --no-cache-dir -e "."
+# ./api/src is mounted as a volume at runtime; the editable .pth file points here
+CMD ["python3", "-m", "uvicorn", "rehearsalhub.main:app", "--host", "0.0.0.0", "--port", "8000", "--reload"]
 
 FROM base AS lint
 COPY pyproject.toml .